Traditionally in cellular networks, a base station (BS), e.g., Node-B or eNB, communicates directly with end user equipment (UE) within the coverage area of the BS (denote these UE as UE1). In relay operations, a Relay or a relay terminal or a Relay Node (RN) first receives information from an eNB on an eNB-to-RN link and then sends out the received information intended for UE that are within the coverage area of the RN (denote these UE generically as UE2 where it is understood that multicasting to a more than one UE's is incorporated). For an “in-band” RN that receives from an eNB on the same band as occupied by the eNB-to-UE1 link, the eNB-to-RN link needs to share resources in time and frequency (or some fraction thereof) with the eNB-to-UE1 link. Conventionally when there is only regular eNB-to-UE1 communications, each UE1 typically receives a control message to determine what resources are allocated to the UE1 and the location of the allocated resources. An RN could, for example, behave like a regular UE (UE1) to receive a control message from an eNB at the same time the eNB transmits a control message to UE1. However, an RN may not be able to receive the control message from the eNB if the RN needs to transmit control information to UE2 at the same time the eNB is transmitting control information to UE1 and the RN.
In the context of the Release-8 specification of Long Term Evolution (LTE) system developed by the Third Generation Partnership Project (3GPP) that is based on Orthogonal Frequency Division Multiplexing (OFDM) for downlink transmissions, the eNB-to-UE1 link consists of typically 1˜3 OFDM symbols at the beginning of each 1-ms sub-frame for control channel, i.e., PDCCH, transmissions. Typically an OFDM symbol comprises an integer number of time units (or samples), where a time unit denotes a fundamental reference time duration. For example, in LTE, the time unit corresponds to 1/(15000×2048) seconds. Thus, the PDCCH transmissions are a first control region with a fixed starting location (contemporaneously) at the first OFDM symbol in a sub-frame. All the remaining symbols in a sub-frame after the PDCCH are typically for data-carrying traffic, i.e., PDSCH, assigned in multiples of Resource Blocks (RBs). Typically, an RB comprises of a set of subcarriers and a set of OFDM symbols. The smallest resource unit for transmissions is denoted a resource element which is given by the smallest time-frequency resource unit (one subcarrier by one OFDM symbol). For example, an RB may contain 12 subcarriers (with a subcarrier separation of 15 kHz) with 14 OFDM symbols with some subcarriers being assigned as pilot symbols, etc. Typically, the 1 ms sub-frame is divided into two slots, each of 0.5 ms. The RB is sometimes defined in terms of a slot rather than a sub-frame. According to the Release-8 specification, the uplink communication between the UE1 and eNB is based on Single-Carrier Frequency Division Multiple Access (SC-FDMA), which is also referred to as Discrete Fourier Transform (DFT)-spread OFDM. Typically, the RN-to-eNB uplink communication may also be preferably done using SC-FDMA. A virtual resource block is a resource block whose subcarriers are distributed (i.e., non-contiguous) in frequency, whereas a localized RB is an RB whose subcarriers are contiguous in frequency. A virtual RB may have improved performance due to frequency diversity. Release-8 UEs typically share resources in the frequency domain (i.e., on an RB-level or in multiples of an RB) rather than in time in any individual sub-frame on the downlink. Similarly, the eNB-to-RN link may also share resources with the eNB-to-UE1 link in the frequency domain, i.e., on an RB-level or in multiples of an RB. A problem may then occur where the RN is transmitting a PDCCH to its users, i.e., UE2, at the beginning of each sub-frame, making the RN unable to receive the PDCCH transmitted by the eNB at the same time.
The various aspects, features and advantages of the disclosure will become more fully apparent to those having ordinary skill in the art upon careful consideration of the following Detailed Description thereof with the accompanying drawings described below. The drawings may have been simplified for clarity and are not necessarily drawn to scale.